Speakers: same brand?

It is very important the center is the same as left and right. Most dialog on HT comes from center (85% of sound) it needs the same character as others. 
 

Certainly does help to have all the same. But it isn’t as important.

Thanks guys. That’s what I was thinking that the voicing of the fronts and center should be the same. An excuse to get more gear!

Not a problem.

I have ESL front and ribbon center. They integrate well.

it must be the same or the sound quality will suffer badly

Some people like to mix up all different kinds of speakers and equipment and that's what it usually sounds like.